Transmission delay circuits



March 29, 1932. I F T ER 1,851,092

TRANSMISSION DELAY CIRCUITS Original Filed June 21. 1927 K V 6' I 2 B E3 a 2 4 C C c I I I I c INVENTOR BY QEFeZfter ATTORNEY 1o v V V'PIOYldGd. a commutator having a plurality Patented Mar. 29, 193 2 i N TS ATE-s if-PATENT omen-f 'CHARLES H. rn'r'rnn, or MILLBURN, NEW 'Jnnsny,AssIe oR ro AMERICAN mnnn- PHONE AND TELEGRAPH COMPANY, A CORPORATION onNEW YO K I r a pplic ,TRANSMISSiON nEIiAYomcUI'r'sQ Original applicationfiled June 21, r927, Serial No. 200,420. Di vided and this animationammary v i 8, 1928, Serial No. 252,831.- 2 p [A I This invention relatesto delay circuits, and particularly to arrangements of aimechanicalnature for introducing delayin the transmission of signals, such asvoice frequency signals which may be transmitted over telephonecircuits. u

-This is a division of applicants copending ation, Serial No. 200,420,filed :J une 21, 192%,, In accordance withthis invention there. is

of segmentsto each one of which acondenser 1s connectedor'associated ina suitable circuit arrangement, so that all of said condensers mayprogressively receive anelectrical charge from an electrical source,such as a voicefrequency signaling source, or an ,lnput c1rcu1t, and sothat said condensers may subsequentlysurrender their electrical chargesin the sameprogress on to a translatm or amplifylng devlce, or an outputcircult, employed inthe transmission'of sigjnals to a distant. point.fThus, in this invention, time delay will be'introduced in the impression.ofthe charges of a plurality of condensers'upon a device or outputcircuit employed in transmission to a distant point. One waytOlIOtIOdHCG time delayin accordancewith the principles of theinvenmutator about its axis and to-thereby pro-f1 tion is to associatewith a commutator a number of brushes of a'typ'e to be subsequently Idescribed, one of which is connected to the electrical source or inputcircuit," and another one of which ls'connected to the-translating oramplifylng device or'output clrcuit.

To carry out the invention with'such a'ppara'r;

tus it is necessary either to-rotate'the comgressively charge thecondensers associated with the segments of the commutator, orto maintainthecommutator stationary in position and to rotatethe brushes aboutit.The

.brushconnected to the input circuit transmits electrical charges tothe'conden'sers iniprogression as a result of thejrel'ative rotation ofthe commutator with respect to that brush,

or viceversa, while the brush connected to the 7 output circuittransmits, in the same pro- ;gression the electrical charges impressedupon these condensers. A third brush may,

various condensers after each charge andl 'dis- "if desired, beprovided'to short circuitthe charge, thereby preparing these condensersand soon; that it is one ofthe It b' comes apparent delay in electricalcircuits by charging a plurality of condensers in progression and by;

discharging these condensers thereafter in .the same progression afterapredetermin'ed interval of time has elapsed;

It is another object of this invention to 1 introduce time delay of adefinite value by suitably spacing brushes associated I with thecommutator, and further, to change the indistance between thesebrushestoag'ain receive a similar charge and to subi se'quently surrender it,

objects of this invention to introduce time A ter'val of delay,asdesired', by changing thev This invention, aswell as its further ob-.

*jects and features, will be better understood represents "one circuitarrangement embody ing the inventionfin Whichja rotatabledis'k orcommutator and stationary brushes are provided,-and Fig.2represents'another embodiment of the invention, in which the disk orcommutator is stationary and thebrushes rotatable with respect tolthe.disk or commutator. A

Referring to Fig 1 of'thedrawings,there V is shown a microphone S inseries relationship with a batteryG so that speech Varia-- 'tions may betranslated into corresponding electrical variationsf These electricalvaria-' tions are then impressed upon an amplifier Afo f any'well-knowntype, preferably of-a vacuum tube type, amplifier amplifying theelectrical variations corresponding to the speech impinging upon themicrophones. The amplifier currents are then transmitted through I atransformer T to' a brush B which is connected to ground through aresistance R andithesecondary winding of transformer T The .brushlB isassociated.

with a commutator or rotatable disk ,K hav- 7 mg a plurality of.segmentseach of which acts; like a; condenser in its capacity to ground.Some of these condensers are designated by the reference character C.Two other brushes, B and B are similarly associated with the commutatorK. As the com- .mutator K revolves about its axis its segcorrespondingvariations in the current flowing between'the plate and filament of that.of the segments of thelcommutator is conbrush B which receives thecharge and transmits it to an output circuit, as will be described morefully hereinafter. 'The third brush B short-circuits each of the condensers through a resistance R as each condenser passes brush B .Theelectricalcharges. which are surrendered to the brush; 13 as a result ofthe rotation of the commutator K cause variations in the potentialimpressed across a resistance R Accordingly, corresponding potentialvariations are effected between the grid and filament of athree-electrode vacuum tube V, which may be employed in this inventionto act as an amplifier. The resistance This in series with a battery Gbetween the grid and filament of vacuum tube V, and these ele- I mentsprovide the bias necessary for the proper operation of vacuum tube V asan A amplifier. The filament of the vacuum tube V is heated to anelectron emitting tempera- 'ture by the flow-of current from a battery CThe potential variations between the grid and filament of the vacuumtube V produce vacuum tube, the circuit interconnecting the plate andfilament including the primary winding of a transformer T and a batteryThese amplified current variations are then transmitted through thetransformer T "toan electrical wave filter F which may be of anywell-known type, preferably of the type described in the patent to G. A.Campbell, No. 1,227,113, dated May 22, 191?. The electrical wave filterF preferably freely transmits currents of frequencies below a :definitelimit, while substantially suppressing currents of frequencies abovethat definite limit. Currents of frequencies above the :definite limitmay be considered distortions,

such as harmonics of the signaling currents,

and. are clearly undesirable. The output of the electrical wave filter Fis then transmitted to an output circuit O,,which may terminate at adistant point,

F ig. 2 shows another embodiment of the inventlon. 1n which thecommutator K is malnt'amed' 1n.a stat onary posit on. Each nected to aseparate condenser C. These condensers are preferably of the samecapacity and have one terminal in common. Sliprings SR SR and SR rotateabout a neednot be repeated.

The operationof the apparatus of F ig. 2 will now be briefly described,it being understood that the general principles of the operation may beapplied equally well to the apparatus of Fig. 1. The output of theamp1ifier A is transmitted through transformer T and through aresistance R slip-ring SR and brush-holder Hi to brush B Sincebrush-holder H is pinned or otherwise permanently. fastened to theslip-ring SR brush B, will rotate about the common axis at the samespeed and progressively make contact with the various condensers C. Theentire potential transmitted by the amplifier A through transformer T isnot impressed uponeach condenser C because of the presence of theresistance R Resistance R decreases each voltage by a definite amount,though these decreased Voltages correspond in every respect to thevoltages transmitted by the amplifier A. Condensers Cretain the chargesimpressed upon them by brush B until brush B makes contact with them.Brush B; is held by brush holder H which is pinned or otherwise fastenedto slip-ring SR Brush B rotates at the same speed as brush B and aboutthe same axis though having an angular. displacement with respect tobrush B the angular displacement determining the time delay to beeffected by the apparatus, Brush B picks up the charges of the variouscondensers in the same progression in which they were charged andimpresses corresponding voltages across the terminals of the resistanceR and'between the grid and filament of the vacuum tube V. Brush Bfollows brush B brush B being held by brush-holder H which is similarlypinned or otherwise fastened to the slip-ring SR Brush B short-circuitseach each condenser in' proper condition to receive an electrical chargeand thereafter to surrender it. It will be obvious that the resistance Ris of a suitable magnitude to thereby prevent the circuits associatedwith the vacuum tube V from sustaining oscillations If each condenserwere short-circuited without series resistance the tendency for theproduccondenser through the resistance R thereby placing,lybelverygreat. V

In orderto showhowthedelay deviceof tion ot-sustained oscillations wouldobvious- 1 this invention may' .be constructed, assume,

, for illustration, a commutator two feet in di- 1 ameter havingQcommutator segments.v about vone-sixteenth of an inch in width,:separated .by very small distances. v Such a commutator would, accordingly,have approximately 1,2 ,segments in its circumference. If it be assumedthat the commutator is stationary l and that the brushes. rotate tenrevolutions per second,-i. e.,'6 )0 revolutions per. minute, then eachbrush would in effect pass 12,000

condensers in asecond, In fact, each condenser would be passed'by-eachbrush tentimes per second; With such a commutator andwithsucha brushspeed, it will be apj-isfactorytransmission could be convenientlyattained .overa band of 4!,000'01 5,000'cycles.

.Thehigher frequencies which become distort- 7 ed and still otherfrequencies introduced' by ,therotation of thebrushes about thecommuta'tator could be, easilyremoved by anelec- .trical wave filter,particularly a ,low pass filter; which'mav be connected as shown in thedraw ngs. If, in a particular arrangement, aset of brushesrotates abouta commutator ten times per second, it is obvious that -.,li] 1S possibleto attain a-maX mum delay 1n transmission of one-tenth'of a second. Ifthe v ,arrangement made fifteen IeVOllltlODS. per .second the maxlmumdelay attainable would I ,beonafifteenth of a second, etc. ,Ifit-becomesdesirable to obtain :delays which are greaterthan the max1mum,'then twoor more of these arrangements m ght be connected 111 l tandem, or, onthe other hand, a greater num- 1 vber. ofsegments-might be provided oneach rother characteristic of the electrical circuit commutator, as bymaking thesesegments narrower or by increasing thediameter of thecommutator. Obviously, by, changing" the brush speedgthe maximum delayattainable may be correspondingly changed within practicallimits.Ingeneral, the interval of time delay is decreased as the brush speed isincreased, and vice versa.

Each voltage transmitted by the amplifier A to each of the condenserspasses through the resistance R If it be assumedthat there exist theideal conditions'of no leakage and no inductance, then the voltageimpressed across each condenser will be i in which E is the voltageoutput of the amplifier A, B is the magnitude of the resistance inseries with the secondary winding of the transformer T C is the capacityof each con- 6 01 E, then denser and}? is the. time during which brushv,B makes contact with each condenser. In I the example givenheretofore, for illustrative purposes, the time t would, at a maximum,beone twelve-thousandth of a second] The impressionlof; such a voltageacrosseach condenser bringsabout its charge at annu- ,--evenra-te, therate of charge being-very great at first and much slower-thereafter. Yetbetween definite limitsthechargeon each con denser is almost directlyproportional to the voltage impressed;there'on.- It vis necessary 7tooperate between theselimitsto prevent If it be assumed that amplitudetortion.

asfollowsf I V f Y C (microf arads) values of its constants. As hasalreadybeen' j The values of'R and C may'thenbe tabulated 1 The valuesof R and C'may with particular regard to the typeof. stru'ctureemployedand the -u-convenient4-and practical I stated,1,-a-fter eachcondenser-becomes charged through.- contact with brush B the-voltageacross each condenseris then impressed upon thegrid circuitofthe-va'cuumtube-Vthrough contact with brushB Thus, the grid circuit of vacuum tubeV will receive a fixed percentage of theoutput of amplifier A, therebyminimizing, the possiblityof amplitude dis- ,tortionp f a L Byvsuitablychoosing convenient values for i the constants of the typeof structureemployed, the timedelay may be made'substam.

tially independent of frequency, amp'litu'de VZwitliinwpracticalglimits. The principles underlying this invention may,for "example,

heap-plied to a radio secrecy system in which aband of frequenciescor-responding to voice frequency signals issub-div'ided into aplurality of sub-bands, the; sub-bands being interchanged in thefrequency spectrumfto tion for similar time intervals. 1

' g The particular values. stated hereinabove are given merely forillustrative purposes and v .;in practiceother values may be chosenwithin '{tl'lfi scope of the invention; Y I

been pointed out n '1 While this invention has ,in certain particulararrangementsmerely for In such "the purpose of'illustration, a isto bedis tinctly understood that the general principles of thisinvention maybe applied to other'and widely varied organizations Without departingfrom the spirit of the invention or the scope of the appended claims.

' What is claimed is: r

The method of delaying the transmission of electrical waves representingspeech, which comprises progressively converting the electrical waves ofvarying amplitude into a plurality of electrical charges which vary asdo the amplitude variations of said Waves, maintaining each of theseelectrical charges undisturbed for a predetermined period of time afterthe beginning of said conversion,

and progressively reconverting the electrical after.

3-, In a system including a plurality of similar surfaces all adjacentto one'another and oppositeto another larger surface, the meth- =od ofdelaying the transmission of signaling currents of varying amplitudesrepresenting speech, which consists in progressively "charging saidsimilar surfaces to potentials with respect to said larger surfacecorresponding to the contlnuous variations in amplitude of the signalingcurrents, retaining the charges on said surfaces a predeterminedinterval of time and in the same relative mag; nitudes, and dischargingall of said surfaces in' the same progression to'reproduce thesignaling'currents having the proper amplitude variations. 1

i. Ina delay system, a plurality of similar electrical: condensers, asource of signaling current of varying amplitude representing speech, afirst moving element Which" progressively chargessaid electricalcondensers inaccordance with the variations in amplitude of thesignaling current, an output circuit, a; second moving elementwhichdisch arges said electrical condensers in the same progression andsuccessively impresses these charges on the output circuit, and'a thirdmoving element which progressively shortcircuits said condensers afterthey have been discharged and after'their charges have been impressed onthe output circuit. 7 i

5. In a delay system, the combination of a plurality of similarelectrical condensers, a source of signaling current of varyingamplitude representing voice frequency signals, an

output circuit; and three moving elements, one of which progressivelycharges said electrical condensers in accordance with the amplitudevariations of the signaling current,

another of which progressively discharges said electrical condensers andimpresses these electrical charges on the output circuit, and the lastof which thereafter short-circuits said electrical condensers.

6. The method of delaying the transmission of electrical waves ofvarying voltages representingvoice frequency signals With apparatusincluding a plurality of similar electrical condensers, which consistsin progresi siv'ely' charging all of said electrical-condenserscorresponding to the voltage variations of the electrical waves, andreconverting said electrical charges into the corresp'onding elec-L-iical waves ofvarying voltage a predeter-.

mined interval of time after the beginning of said transmission.

'7; A transmission delay system comprising a commutator having aplurality of segments, a plurality of condensers, one condenser be-.

in g connected to each segment, means for"pr0- gressivel'y charging allof said condensers in accordance with the-variations of speech signalingwaves, and means for reconvertingthe charges of all of said condensersin the same progression into the correspondingvariations of speechsignaling waves a predetermined interval of time after said charges havebeen impressed upon said'condensersi 8'. A wave transmission systemcomprising, a plurality of condensers, three brushes which rotate at thesame speed about a common axis and which are separated from each otherby predetermined distances alonga circumference'of said axis, a sourceof speech signals,

means associated with one of said brushes for progressivelychargingsaid'condensers in accordance with said signals, meansassociated with another of said brushes for progressive- "ly'discharging said-condensers in-ordert'o reproduce said signals, andmeans associated with the third of said brushes for progressivelyshort-circuitingsaid condensers.

In testimony whereof, I have signed my name to this specification this6th day of. February, 1928. is

CHARLES FETTER.

